mv circuit breaker guide - ansi vs iec comparison.pdf

Appendix 3: IEC - ANSI comparison

IEC 56-1987 - ANSI C37-06 1987 COMPARISON

CONTENTS page

1 - Rated voltage 3

2 - Rated isolating level 3

3 - Rated voltage during normal running 4

4 - Allowable short time current 4

5 - Allowable current peak value and making capacity 4

6 - Rated short-circuit time 5

7 - Rated voltage supplying closing, opening and auxiliary circuit devices, 5

8 - Rated frequency 5

9 - Rated operating cycle short-circuit breaking capacity 6

10 - Associated transient recovery voltage 8

11 - Rated operating cycle 9

12 - Rated phase unbalance breaking capacity 10

13 - Rated off-load cable breaking capacity 11

14 - Rated off-load line breaking capacity 11

15 - Rated unique capacitor bank breaking capacity 12

16 - Rated stage capacitor bank breaking capacity 13

17 - Rated capacitor bank making capacity 13

18 - Rated low inductive current breaking capacity 14

19 - Normal operating conditions 15

20 - Electrical endurance 16

21 - Mechanical endurance 16

22 - Construction 16

23 - Derating 17

24 - Coordination of rated values 17/18

Medium v olta ge cir cuit breaker tec hnical guide

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Appendix 3: IEC - ANSI comparison(cont’d)

The following comparison is based on different circuit breaker characteristics.

Summar y of main diff erences

theme ANSI IECasymmetric 50% with 30% withoutbreaking capacity current deratingon terminal faults derating

isolating level: impose chopped impact wave waves for outdoor

equipment115% Uw/3 s129% Uw/2 s

allowable short time current 2.7 Isc 2.5 Iscpeak value

Transient Recovery approximatelyVoltage (1) 2 times stricter

electrical endurance 4 times K.S.Isc 3 fois Isc

mechanical endurance 1 500 to 10 000 2 000depending on Ua and Isc

motor overvoltages no text type testcircuit

(1) The ANSI peak voltage is 10% higher than the voltage defined by the IEC.The E2/t2 gradient is 50% steeper than the Uc/t3 gradient.

On the other hand, the steepest part of the curve is the initial part, where theSF6 is reconstituted. The two standards easily allow SF6 to be reconstituted.


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1 - RATED VOLTAGE Un (kV)

According to IECStandardized values for Un (kV) : 3.6 - 7.2 - 12 - 17.5 - 24 - 36 kV

According to ANSIThe ANSI standard defines a grade and a “voltage range factor K” whichdefines a rated voltage range with constant po wer.

Standar dized values f or Un (kV)Indoor equipment Outdoor equipment

2 - RATED ISOLATING LEVEL

According to IEC

standardized wave 1.2/50 µs

According to ANSI

Indoor equipment Outdoor equipment

BIL : Basic Insulation LevelOutdoor equipment is tested withchopped waves.The impact wave withstand is equal to:1.29 BIL for a time tc = 2 µs1.15 BIL for a time tc = 3 µs

chopped wave according to ANSI for outdoor equipment

1009070

3010 t (µs)

Upeak (%)

tc

grade impact wave industrialwithstand frequency(BIL) withstand

(kV) (kV) (kV rms)

15.5 110 50

25.8 125 60150

38 150 80200

grade impact wave industrialwithstand frequency(BIL) withstand

(kV) (kV) (kV rms)

4.16 60 19

7.2 95 36

13.8 95 36

38 150 80

10090

50

101.2 µs

t (µs)

50 µs

Upeak (%)rated impact wave industrialvoltage withstand frequency

(BIL) withstand(kV) (kV) (kV rms)

7.2 60 20

12 75 28

17.5 95 38

24 125 50

36 170 70

grade K(kV)

15.5 1

25 1

38 1

grade Umax. Umin. K(kV) (kV) (kV)

4.16 4.76 3.85 1.24

7.2 8.25 6.6 1.25

13.8 15 11.5 1.3

38 38 23 1.65

K = Umax.Umin.


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3 - RATED VOLTAGE DURING NORMAL RUNNING

According to IECRated current values: 400 - 630 - 1250 - 1600 - 2500 - 3150 A

According to ANSIRated current values: 1200 - 2000 - 3000 A

4 - ALLOWABLE SHORT TIME CURRENT

According to IECRated short-circuit breaking capacity values (kA): 6.3 - 8 - 10 - 12.5 - 16 - 20 - 25 - 31.5 - 40 - 50 - 63 kA

According to ANSIRated short-circuit breaking capacity values (kA):

Outdoor equipment: 12.5 - 20 - 25 - 31.5 - 40

Indoor equipment

5 - ALLOWABLE CURRENT PEAK VALUE AND MAKING CAPACITY

According to IECThe allowable short time current peak value is equal to 2.5 Isc.

According to ANSIThe allowable short time current peak value is equal to 2.7 K Isc peak value;1.6 K Isc root mean square value.

K: voltage factor.

grade breaking capacityI at Umax. KI at Umin.

(MVA) (kA) (kA)

250 29 36

350 41 49

500 18 23

750 28 36

1000 37 48

1500 21 35

2750 40 40


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6 - RATED SHORT-CIRCUIT TIME

According to IECThe rated short-circuit time is equal to 1 or 3 seconds.

According to ANSIThe rated short-circuit time is equal to 3 seconds.

7 - RATED VOLTAGE SUPPLYING OPENING AND CLOSING DEVICES ANDAUXILIARY CIRCUITS

According to IECAuxiliary circuit supply voltage values:■ in direct current (dc): 24 - 48 - 60 - 110 or 125 - 220 or 250 volts.■ in alternating current (ac): 120 - 220 - 230 - 240 volts.

The operating voltages must be within the following ranges:■ motor and closing trips: -15% to +10% of Un in dc and ac■ opening trips:-15% to +10% of Un in ca; -30% to +10% of Un in dc■ minimum voltage opening trips.

U0% 35% 70% 100%

According to ANSIAuxiliary circuit supply voltage values:■ in direct current (dc): 24 - 48 - 125 - 250 volts.■ in alternating current (ac): 120 - 240 volts.

The operating voltages must be within the following ranges:

Motor and closing trips Opening trips

8 - RATED FREQUENCY

According to IECRated frequency: 50 Hz.

According to ANSIRated frequency: 60 Hz.

voltage voltage range

24 Vdc 14 V to 28 V

48 Vdc 28 V to 56 V

125 Vdc 70 V to 140 V

250 Vdc 140 V to 280 V

120 Vac 104 V to 127 V

240 Vac 208 V to 254 V

voltage voltage range

48 Vdc 36 V to 56 V

125 Vdc 90 V to 140 V

250 Vdc 180 V to 280 V

120 Vac 104 V to 127 V

240 Vac 208 V to 254 V

the tripping coilmust not action

the circuit breaker tripsand cannot be reclosed


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9 - RATED OPERATING CYCLE SHORT-CIRCUIT BREAKING CAPACITY

ANSI specifies 50% asymmetry and the IEC 30%. In 95% of applications, 30% is sufficient. When 30% is too low, this means that the applicationshave specific requirements (nearby generators) for which the asymmetrymay be higher than 50%. For the two systems of standards, the designermust check the circuit breaker breaking capacity.The difference is not important since even if the asymmetry factor “S” is nottaken into account, it remains equal to 10%.

According to IECThe short-circuit breaking tests must satisfy the following 5 test cycles (cf. § 5 - 10)

According to ANSIThe circuit breaker must be able to break: ■ the rated short-circuit current at the rated maximum operating voltage,■ K times the short-circuit current (maxi symetrical interrupting capabilitywith K: voltage range factor) at the rated maximum operating voltage (maxivoltage/K),■ between two currents obtained through the relation:

A constant breaking power is thus obtained (in MVA) over a given voltagerange. Furthermore, the asymmetrical current will depend on the followingtable when S = 1.1 for MG circuit breakers.

ratio S1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1

00

0.5 1 2 3 40.006 0.017 0.033 0.050 0.087 seconds

cycles

circuit breaker contact parting timesum of 1/2 cycle tripping delay plus the opening time of the individual breaker

asymmetrical interrupting capability = S x symetrical interrupting capability, both at specified operating voltage

symetrical interrupting capability at specified operating voltage = 1.0

maxi symetrical currentrated short-circuit current

= rated maxi voltagerated voltage

= K

cycle % Isym. % aperiodic no. component

1 10 ≤ 20

2 20 ≤ 20

3 60 ≤ 20

4 100 ≤ 20

5* 100 30

*for circuit breakers opening in less than 80 ms

IEC:Iasym. = Isym. 1 + 2 A2 = 1.08 Isym. A = 30%

ANSI: Iasym. = Isym. 1 + 2 A2 = 1.22 Isym. A = 50%


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Rated short-circuit breaking capacity values (kA): cf. § 4

The short-circuit breaking tests must satisfy the following 14 test cycles where:I: symmetrical breaking capacity at maxi. voltageR: Reclosing factor

K: voltage range factor =

V: rated maximum voltage

Example : Isc = 40 kAasymmetry % = 50%Iasym. = 1.1 x 40 = 44 kA

Cycle 6 will thus be tested at 36 kA + 50% asymmetry giving 44 kA oftotal current.

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S = asymmetrical factor =Iasym.

Isym. = 1.1 for MG circuit breakers

K = Vmax. Vmin.

cycle broken % aperiodic no. current component

1 10 50 - 100

2 30 < 20

3 60 50 - 100

4 100 < 20

5 KI to V/K < 20

6 SI to V 50 - 100

7 KSI to V/K 50 - 100

8 electrical endurance

9/10 reclosing cycle at RSI and RKSI

11 C - 2 s - O to KI

12 rated Isc timeIsc = KI during 3 s

13/14 single-phase testsat KI and at KSI (0.58 V)

Isym. = 441 + 2 (50%)2

= 441.22

= 36 kA


10 - ASSOCIATED TRANSIENT RECOVERY VOLTAGE (TRV) (cf. § 5.11)

The ANSI peak voltage is 10% higher than the voltage defined by the IEC,the E2/t2 gradient is 50% steeper than the Uc/t3. On the other hand, thesteepest part of the curve is the initial part, where the SF6 is reconstituted.The two standards easily allow SF6 to be reconstituted.The ANSI t2 values are valid for outdoor type circuit breakers. Other t2 valuesfor indoor type circuit breakers are being worked on, and these values aremuch closer to the IEC values.

According to IECRepresentation of a specified TRVby a reference plotting with 2parameters and by right-handsegment defining a delay.

td: delay timet3: time taken to reach UcUc: TRV peak voltage in kV

☞ note: the TRV depends on theasymmetry. It is given for anasymmetry of 0%.

Rated TRV valuerated voltage TRV value time delay stepping up speed(Un in kV) (Uc in kV) (t3 in µs) (td in µs) (Uc/td in kV/µs)

7.2 12.3 52 8 0.24

12 20.6 60 9 0.34

17.5 30 72 11 0.42

24 41 88 13 0.47

36 62 108 16 0.57

According to ANSI

E2: TRV peak voltageE2 peak = 1.88 max. rated UE2 rms = 1.5 max. phase - earth Ut2 = 36 ms for 15.5 kV

= 52 ms for 25.8 kV= 63 ms for 38 kV

TRV = E2/t2 x 1.14t (µs)

U (kV)

E2

shape: 1 - cos

0

t 2

td = 0.15 t3Uc = 1.4 • 1.5 • 23

• U

t (µs)

U (kV)

t d

Uc

0

t 3


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11 - RATED OPERATING CYCLE

According to IECThere are three rated operating cycles:slow: O - 3 mn - CO - 3 mn - COfast 1: O - 0,3 s - CO - 3 mn - COfast 2: O - 0.15 s - CO - 15 s - CO.

☞ note: other cycles may be required.

Closing-opening c ycle

Automatic rec losing c ycle

According to ANSIOnly one rated operating cycle: CO - 15 s - CO

time

initiation of short-circuit

energization of trip circuit

parting of primary arcing contacts

extinction of arc on primary contacts

parting of primary arcing contacts

primary arcingcontacts make

* reclosing time is the time interval between energization of the trip circuit and making of the primary arcing contacts.

reclosing time*

interrupting time

trippingdelay

openingtime

arcingtime

contactparting time

reclosing time

opening-closing time

final extinction of arc in all poles

arcing contact separationin all poles and order C

energization of opening trip

contacts touch in primary pole

start of current circulation in all poles

contacts touch in all poles

remaking time

breaking-making time

current circulation current circulation

opening position

time

closing position contact displacement

current circulation

openingposition

closing positioncontact displacement

time

energization of closing circuit

start of current circulation in primary pole

arcing contact separation in all poles

contacts touch in all poles and order O

final arc extinction in all poles

making-breaking time

closing-opening time


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O represents an opening operation.CO represents a closing operationimmediately followed by an openingoperation.

O

Isc

t

time

t '

In

C O C O

rated operating cycle according toIEC: O - t - CO - t' - CO


12 - RATED UNBALANCE PHASE BREAKING CAPACITY

According to IEC (cf. § 5 - 12)In practice, the circuit breaker is required to break a current equal to 25%of the fault current at the terminals, under a voltage equal to double ofthe voltage in relation to the earth.

The industrial frequency recovery voltage (TRV) is equal to:■ for networks where the neutral is direct to the earth.■ for other networks.Un is equal to the rated circuit breaker voltage.

Peak TRV values for networks where the neutral is not earthed:

rated voltage TRV value time stepping up speed(Un in kV) (Uc in kV) (t3 in µs) (Uc/td (kV/ µs)

7.2 18.4 104 0.18

12 30.6 120 0.26

17.5 45 144 0.31

24 61 176 0.35

36 92 216 0.43

According to ANSIIn practice, the circuit breaker is required to break a current equal to 25%of the fault current at the terminals, under a voltage equal to the voltagein relation to the earth.

Uc = 1.25 • 2.5 • 32

• Un

2.5 3 Un

2.0 3 Un


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13 - RATED OFF-LOAD CABLE BREAKING CAPACITY (cf. § 5 - 13)

According to IECThe rated off-load cable breaking capacity specification for a circuit breakeris not obligatory and is considered as unnecessary for voltages ≤ to 24 kV.

Normal rated off-load cable Allowable maximum breaking capacity values overvoltages

According to ANSICf. unique battery breaking.

14 - RATED OFF-LOAD LINE BREAKING CAPACITY

According to IECThe rated off-load line breaking capacity specification is limited to circuitbreakers for operating three-phase overhead lines with a rated voltage ≥ 72 kV.

According to ANSI

Indoor equipment Outdoor equipmentmax. rated rated off-load linevoltage breaking capacity(kV) (A rms)

15.5 100

25.8 100

38 100

max. rated rated off-load linevoltage breaking capacity(kV) (A rms)

4.76 1

8.25 1

15 2

38 5

rated overvoltagevoltageU (kV)

7.2 4.5

12 4

17.5 4

24 3.8

36 3.8

rated rated off-load cablevoltage breaking capacityU (kV) Ic (A rms)

7.2 10

12 25

17.5 31.5

24 31.5

36 50


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pu (kV) =Un 23


15 - UNIQUE CAPACITOR BANK BREAKING CAPACITY

According to IECThe capacitor breaking capacity specification is not obligatory. The capacitorbreaking capacity is equal to 0.7 times the value of the device’s rated current.

The maximum overvoltage value allowable is equal to 2.5 pu, in other words:

According to ANSIThe capacitor breaking capacity is:

For indoor equipment

For outdoor equipmentrated capacitor breakingvoltage capacity Umax. (kV) (A)

15.5 400

25.8 400

38 250

rated short-circuit rated capacitor breakingvoltage breaking capacity current capacityUmax. (kV) (kA) (A) (A)

4.76 29 1200 630

29 2000 1000

41 1200/2000 630

41 3000 1000

8.25 33 1200 630

33 1200 1000

15 18 1200 630

18 2000 1000

28 1200 630

28 2000 1000

37 1200 630

37 2000 1000

37 3000 1600

38 21 1200/2000/3000 250

40 1200/3000 250

2.5 x Un 23

with pu = Un 23

L

U C

A B

Ic

G

rated capacitor breakingcurrent capacity(A) (A)

400 280

630 440

1250 875

2500 1750

3150 2200


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16 - RATED STAGE CAPACITOR BANK BREAKING CAPACITY

According to IECThe rated stage capacitor bank breaking capacity specification is not obligatory.

According to ANSICf. unique capacitor bank § 15.

17 - RATED CAPACITOR BANK MAKING CAPACITYThe rated capacitor bank making capacity is the peak value of the currentwhich the circuit breaker must be able to make under its rated voltage andwith an inrush current frequency appropriate to the operating conditions.

According to IECThe rated capacitor bank making capacity values must be higher than themake current value (see capacitor application).When operating, the inrush current frequency is normally in the 2 - 5 kHz zone.

According to ANSIThe ANSI standard fixes the inrush current value and frequency (back to back capacitors).

For indoor equipment For outdoor equipmentvoltage current inrush current Umax. Ipeak frequency(kV) (A) (kA) (kHz)

15.5 400 20 4.24

25.8 400 20 4.24

38 250 20 4.24

voltage current inrush current Umax. Ipeak frequency(kV) (A) (kA) (kHz)

4.76 600 15 2

1000 15 1.27

8.25 600 15 2

1000 15 1.27

15 600 15 2

1000 15 1.27

1600 25 1.33

38 250 18 6

250 25 8.48


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UG

X1

C1 C2 Cn

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18 - RATED LOW INDUCTIVE CURRENT BREAKING CAPACITY (cf. § 5 - 18)

According to IEC (cf. § 4.112 - IEC 56 - 87)This subject is being studied.

Motor isolating le velsThe IEC 34 stipulates motor isolating levels.The industrial frequency and impact withstand tests are given in the tablebelow (table 1: inductive current breaking, chapter 3, part B, CIGRE).

rated isolating levels for rotating equipment

According to ANSINon standard.

isolation test at 50 (60) Hz rms impact test BIL

between turns (4 Un + 5) kV 4.9 pu + 5 = 31 kV to 6.6 kV(50% on a sample)rise time 0.5 µs

in relation to the earth

(2 Un + 1) kV2 Un + 1 ⇒ 2 (2 Un + 1) ⇒ 014 kV ⇒ 28 kV ⇒ 0

(4 Un + 5) kV4.9 pu + 5 = 31 kV to 6.6 kVrise time 1.2 µs

1 kV/s

1 mn0

t



Appendix 3: IEC - ANSI comparison(cont’d) A) TEMPERATURE

According to IEC

Derating should be provided for allequipment operating in differentconditions from those describedabove (see derating chapter).

B) ALTITUDE

According to IECThe altitude must not be higher than1000 metres, if higher derating isnecessary.

C) HUMIDITY

According to IECaverage relative indoorhumidity value equipmenttime period

24 hours 95%

1 month 90%

0 °C installationimmediate ambient indoor outdoortemperature

minimum -5 °C -25 °C

maximum +40 °C +40 °C

daily average 35 °C 35 °Cmaximum value


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19 - NORMAL OPERATING CONDITIONSThe equipment is designed to operate normally in the following conditions:

According to ANSI0 °C installationimmediate ambient temperature

minimum -30 °C

maximum +40 °C

According to ANSIThe altitude must not be higher than3300 feet (1000 metres), if higherderating is necessary.

According to ANSINo specific constraints.

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20 - ELECTRICAL ENDURANCE MG circuit breakers ensure 15 times Isc minimum. The IEC and ANSI standardsimpose values which are far too low since they take account oil breaking circuitbreakers.These values are not important and if so required by the customer, the valueof the considered device should be supplied.

According to IECThe electrical endurance is equal to 3 times Isc.

According to ANSIThe electrical endurance is equal to 4 times K.S.IscIsc: symmetrical breaking capacity at maxi voltageS: asymmetry factorK: voltage range factor

21 - MECHANICAL ENDURANCE

According to IECThe mechanical endurance is 2 000 operating cycles.

According to ANSIThe mechanical endurance is between 1 500 and 10 000 operating cyclesdepending on the voltage and breaking capacity.

22 - CONSTRUCTION

According to IECThe IEC does not impose any particular constraints. The manufacturer ishowever responsible for determining what kind of material is needed(thickness, etc.) in order to ensure a solid performance.

According to ANSIThe ANSI imposes a thickness of 3 mm for sheet metals.




23 - DERATING

According to IECRefer to paragraph 6 of technical guide.

According to ANSIThe ANSI C37 04 standard provides for temperatures higher than 1 000 metres:■ a correction factor for the voltage applicable on the rated isolating leveland on the rated maximum voltage.■ a correction factor for the rated current during normal running. The correction factor table depending on the altitude(Altitude Correction Factors : ACF)altitude ACF for ACF for

voltage continous current(ft) (m)

3 300 1 000 1.00 1.00

5 000 1 500 0.95 0.99

10 000 3 000 0.8 0.96

☞ note: for “sealed system” type circuit breakers, it is not necessary toapply the ACF voltage on the rated maximum voltage.

24 - COORDINATION OF RATED VALUES

According to IEC

rated rated rated current during voltage short-circuit normal running

breakingcapacity

U (kV) Isc (kA) In (A)

3.6 10 40016 630 125025 1250 1600 250040 1250 1600 2500 3150

7.2 8 40012.5 400 630 125016 630 1250 160025 630 1250 1600 250040 1250 1600 2500 3150

12 8 40012.5 400 630 125016 630 1250 160025 630 1250 1600 250040 1250 1600 2500 315050 1250 1600 2500 3150

17.5 8 400 630 125012.5 630 125016 630 125025 125040 1250 1600 2500 3150

24 8 400 630 125012.5 630 125016 630 125025 1250 1600 250040 1250 1600 2500 3150

36 8 63012.5 630 125016 630 1250 160025 1250 1600 250040 1250 1600 2500 3150


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According to ANSI

rated short-circuit rated short-circuit rated current duringmaximum breaking minimum breaking normal runningvoltage capacity voltage capacity

at Umax. at Umin.Umax. (kV) Isc (kA) (kV) Isc (kA) In (A)

4.76 18 3.5 24 120029 3.85 36 1200 200041 4 49 1200 3000

8.25 7 2.3 25 600 1200 200017 4.6 30 120033 6.6 41 1200 2000

15 9.3 6.6 21 12009.8 4 37 120018 11.5 23 1200 200019 6.6 43 1200 200028 11.5 36 1200 200037 11.5 48 1200 3000

15.5 8.9 5.8 24 60018 12 23 120035 12 45 120056 12 73 2000 3000 4000

25.8 5.4 12 12 60011 12 24 1200

38 22 23 36 1200 300036 24 57 1200


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